Location systems have become mainstream devices in the last two decades, first with the introduction of low-cost GPS devices and later on with the almost worldwide adoption of smart phones having navigation functionality.
More recently indoor location systems are receiving increased attention. Several indoor location systems are known, systems based on, infrared (IR), ultrasound, video surveillance, and RF signals.
Also multi-modal systems appear to attract quite some attention, such as the “Headio” system, as presented in “Headio: Zero-Configured Heading Acquisition for Indoor Mobile Devices Through Multimodal Context Sensing”, by Zheng Sun, et al. The latter system combines information from gravity sensors and magnetometer sensors as found in a smart phone with camera data captured therewith. In the Headio system the front facing camera is used to image the ceiling, a ceiling which quite often has straight edges which can be used as a further modality for orientation.
However, not all ceilings have such “clearly visible edges”, and in situations where these are lacking the system may not perform well.